William Henry Reed MVO (29 July 1875 – 2 July 1942; his birth year is often given in error as 1876) was an English violinist, teacher, composer, conductor and biographer of Edward Elgar. He was leader of the London Symphony Orchestra for 23 years (1912–1935), but is best known for his long personal friendship with Elgar (1910–1934) and his book Elgar As I Knew Him (1936), in which he goes into great detail about the genesis of the Violin Concerto in B minor.
The book also provides a large number of Elgar's sketches for his unfinished Third Symphony, which proved invaluable sixty years later when Anthony Payne elaborated and essentially completed the work, although Reed wrote that in his view the symphony could not be completed.
His name appears in various forms: William Henry Reed, W. H. Reed, W. H. "Billy" Reed, Billy Reed and Willie Reed. He was known to his friends as Billy.